Heat radiator composed of a combination of a graphite-metal complex and an aluminum extruded material

ABSTRACT

To provide a heat radiator that is useful for an LED package, high-load semiconductor, high-load capacitor or an integrated circuit board composed of a combination thereof that assumes a short lifetime and falls at high temperatures. 
     To constitute a heat radiator that is low in cost, superior in mechanical strength, and, furthermore, superior in heat radiating effect, by combining a graphite-metal complex that is good in heat diffusivity and an aluminum heat sink that is large in heat radiating surface area.

PRIORITY CLAIM AND CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage application of International Application No. PCT/US2008/88461, filed Dec. 29, 2008, which claims priority from Japanese Patent Application No. 2008/233604, filed Sep. 11, 2008. The contents of both of these applications are incorporated by reference herein in their entirety.

BACKGROUND

Graphite-based metal complex materials are known wherein metal is dispersed in a graphite molding sintered from a molding by unidirectional pressure using a metal complex material, extruded molding, or cold isostatic pressure molding wherein a metal matrix and graphite particles or graphite fibers have been dispersed as a material in a graphite-metal complex incorporating a graphite material. (Japanese Patent Application H11-321828, Patent Application 2001135551)

On one hand it is known that with complexes that incorporate graphite, when the thermal diffusivity of material normally used as heat transfer media such as aluminum, copper or aluminum nitride that have a high thermal diffusivity of 1.5-3 cm²/sec is compared to 0 7-1.0 cm²/sec, the heat spreading performance thereof is superior.

On the other hand, with complexes that incorporate graphite, such as complexes with aluminum in which a graphite extruded material has been used, the bend strength is 30-40 Mpa, the elastic coefficient thereof is low at 12 Gpa, and, in comparison to regularly used metals such as aluminum, magnesium, titanium, copper, or iron, etc. a mechanical strength of 1/10 or less is assumed. In addition, the provision of an aluminum extruded material for heat sink is low in cost as it is mass produced, while graphite-metal complexes are comparatively high in cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a graphite-metal complex and aluminum heat sink (flat board type).

FIG. 2 is a diagram of a graphite-metal complex and aluminum heat sink (column type).

FIG. 3 is a diagram of a graphite-metal complex aluminum heat sink (prism type).

FIG. 1 of FIG.-1 is a flat board type metal complex (2) and aluminum heat sink (3). FIG. 2 and FIG. 3 are respectively a column type and graphite-metal complex (2) and aluminum heat sink (3).

DETAILED DESCRIPTION

The invention relates to a heat radiator composed of a combination of a suitable graphite-iron complex and aluminum extruded material on an LED package, high-load semiconductor, high-load capacitor or an integrated circuit board composed of a combination thereof that assumes a short lifetime and fails at high temperatures.

The purpose of the invention is to take into account the aforementioned problems and provide a heat radiator that, while maintaining the properties of good thermal diffusivity of graphite metal complexes, reinforces the weak mechanical properties that are a drawback thereof, and furthermore, is lower in cost.

The inventor reached an invention summarized as follows below that positively achieves the aforementioned purpose, by devising a combination of the material used.

A heat radiator wherein a graphite-metal complex obtained by pressure-impregnating aluminum, copper or an alloy thereof into a graphite molding incorporating a 50-92 volume % of graphite powder by squeeze casting is cut into board shapes or column shapes, etc., which are aligned and arrayed into the shape of a heat sink composed of an extruded material of aluminum or aluminum alloy.

A heat radiator wherein aluminum, copper or an alloy thereof is pressure-impregnated by squeeze casting into a molding incorporating a 50-92% combination of short fiber material of chopped graphite fibers and man-made graphite, and the obtained graphite-metal complex is cut and arrayed so that it properly conforms to the shape of a heat sink composed of an extruded material of aluminum or aluminum alloy.

The molding method of the molding graphite powder of chopped graphite fibers incorporating graphite powder is one of molding by unidirectional pressure, using an extruded molding or cold.

The invention enables the utilization of the good heat diffusivity of a graphite-metal complex, with the weakness in mechanical strength of a graphite-metal complex reinforced by bringing it into contact with an aluminum or aluminum alloy metal extruded material. In addition, low cost is achieved by preparing everything with a graphite-metal complex.

Thus, an economically superior heat radiator is provided wherein the heat generated by an LED package, high-load semiconductor, high-load capacitor or integrated circuit board is efficiently diffused by the graphic-metal complex, and the heat is radiated by a heat sink of strong aluminum alloy from fins having a large surface area.

The manufacturing method of the graphite-metal complex is pressure-impregnation by squeeze casting. The graphite used during this may be one in which man-made graphite is extruded with tar, pitch or an organic resin, one made by cold isostatic molding or one molded by unidirectional pressure with a die, which is then ultimately heat-treated at 2500° C. or more, and consequentially close to 100% forms a graphite system.

In addition, during this, chopped graphite fiber may be incorporated.

As described above, the obtained graphite-metal complex is superior for machining, and can be easily worked into board, column or prism shapes, etc.

On one hand, various shapes of aluminum extruded materials are prepared. These consist of fins and parts that bundle these, and, as described by FIG. 1 below, 1 is a heat radiator, 2 is a graphite-metal complex, 3 is a heat sink of aluminum extruded material, and 2 is a board in contact with 3. In FIG. 2, the 2 graphite-metal complex is column-shaped, the outer surface thereof coming into contact with the inner surface of the 3 aluminum extruded material. In FIG. 3, the 2 graphite-metal complex is prism-shaped, the four-sided surface thereof coming into contact with the inside surface of the 3 aluminum extruded material.

The connection method of the graphite-metal complex and heat sink may be a shrink-fit method, as the thermal expansion rate of the graphite-metal complex is 7×10⁻⁶ 1/K, and that of the aluminum is 23×10⁻⁶ 1/K in FIG. 2 and FIG. 3, for example. A set screw with silicon grease between the graphite-metal complex and heat sink, or plating and soldering, on both sides, may be used with the embodiment in FIG. 1.

The aluminum heat sink used in the invention is not limited to an extruded material, and a die-cast, casted or forged materials, etc. may be utilized. Thus, the substance may be an aluminum alloy, but a JIS A 1000 or JIS A 6000 series alloy is more suitable as it is both workable and high in thermal conductivity.

The types of graphite used in the invention are natural graphite and man-made graphite, and commercially-available graphite blocks are acceptable.

A 50%-95% volume fraction may be used for the graphite in the graphite-metal complex. If it is 50% or less, the heat diffusivity rate is low, and so is not suitable for the heat radiator in the invention.

65%-95% is more preferable.

The metal used in the graphite-metal complex is aluminum, an aluminum alloy, copper or a copper alloy. The aluminum alloy used may be of a JIS wrought material series or a JIS cast metal material series, etc. However, an alloy with a low melting point is preferred. As for copper alloy, a JIS C 1000 series-7000 series wrought copper materials, etc. may be used.

A heat radiator obtained as described above achieves a more efficient heat radiator, by using a graphite-metal complex superior in heat diffusivity at the position that makes contact with a heat source, and combining an aluminum heat sink of large heat radiating surface area at the position that makes contact with the graphite-metal complex.

In addition, the aforementioned heat radiator is capable of functioning as a structure by reinforcing the weak mechanical strength of the graphite-metal complex with an aluminum heat sink.

Below, we will describe an example in detail.

The size of an electrode graphite block (Tokai Carbon UHP) remains at 150 mm×200 mm×250 mm at 700° C. in an argon atmosphere, while a JIS-AC3 A aluminum alloy melts at 700° C. These are introduced into a die for squeeze casting, and casting is completed at a pressure of 60 Mpa.

A graphite-metal complex was obtained from the casting, which was then cut into boards 2 mm thick in length and had sides 20 mm in size, and, after 4 W LED had been mounted on top of these, they were brought into contact with the 30 mm×25 mm of an aluminum (JIS A 6063 extruded material) heat sink with 10 fins that are 10 mm in length, and when they were energized 333 mA with 12 V and the temperature was measured after one hour, the LED tops were 38° C. and the heat sink fins were 26° C. Furthermore, the room temperature was 22° C.

Instead of the graphite-metal complex 111 the aforementioned Working Example 1, a JIS A 1050 board of the same size was used, and when the same test was performed, the LED tops were 105° C. and the heat sink fins were 70° C.

Instead of the graphite-metal complex in the aforementioned Working Example 1, a JIS A 1050 board of the same size was used, in reverse, a heat sink was prepared of the same shape as the aluminum heat sink in Working Example 1 by processing a graphite-metal complex, and when the same test was performed, the LED tops were 98° C. and the heat sink fins were 54° C.

A 150 mm×200 mm board 3 mm thick was prepared from the graphite-metal complex in the above example, and then screwed onto the 2 mm thickness of the flat board section of an aluminum heat sink with the same 150 mm×200 mm size with 30 fins that are 30 mm tall. A 120 W heat discharge integrated circuit board was disposed on a graphite-metal complex board, and when a temperature measurement was taken after two hours, the graphite-metal complex board was 45° C., and the fins of the aluminum heat sink were 35° C.

When a temperature measurement was taken under the same conditions of the flat board section of an aluminum heat sink as in the example above with a thickness other than 5 mm, the temperature of the flat board section was 97° C. and the fins were 70° C.

The heat radiator composed of a combination of a graphite-metal complex and an aluminum extruded material, etc. in the invention combines those that have superior heat diffusivity and those in which a low-cost aluminum heat sink have a large heat radiating surface area, and therefore is effective in radiating the heat of an LED package, high-load capacitor or an integrated circuit board composed of a combination thereof, and is useful in a wide range of industrial fields. 

1. An article of manufacture comprising: a heat radiator wherein aluminum, copper or an alloy thereof has been pressure-impregnated by squeeze casting into a graphite molding that incorporates a 50-92 volume % graphite powder, and the obtained graphite-metal complex is cut into board shapes and brought into contact with the part of the flat or curved sections of a heat sink composed of an extruded material of aluminum or aluminum alloy.
 2. The article of manufacture as recited in claim 1, wherein the graphite used to produce the heat radiator is derived from a molding by unidirectional pressure, using an extruded molding, a cold isostatic pressure molding and a die.
 3. An article of manufacture comprising: a heat radiator wherein aluminum, copper or an alloy thereof has been pressure-impregnated by squeeze casting into a graphite molding that incorporates a 50-92 volume % of combined chopped fibers of graphite and man-made graphite, and the obtained graphite-metal complex is cut into board shapes and brought into contact with the part of the flat or curved sections of a heat sink composed of an extruded material of aluminum or aluminum alloy.
 4. The article of manufacture as recited in claim 3, wherein the graphite used to produce the heat radiator is derived from a molding by unidirectional pressure, using an extruded molding, a cold isostatic pressure molding and a die.
 5. An article of manufacture comprising: a heat radiator wherein aluminum, copper or an alloy thereof has been pressure-impregnated by squeeze casting into a graphite molding that incorporates a 50-92 volume % graphite powder, and the obtained graphite-metal complex is cut into column shapes or prism shapes, which are disposed in the middle of a heat sink composed of an extruded material of aluminum or aluminum alloy, wherein fins of the heat sink have been radially arrayed, and the column or prism sides touch the heat sink
 6. The article of manufacture as recited in claim 5, wherein the graphite used to produce the heat radiator is derived from a molding by unidirectional pressure, using an extruded molding, a cold isostatic pressure molding and a die. 